(a) Core/shell nanoparticle geometry: (b) A cross section of the optical intensity distribution around the core/shell nanoparticle. (c,d) Internal optical intensity enhancement as a function of core radius and thickness when the size-dependent values of the metal’s dielectric functions are used. (c) gold, (d) silver shells.

Material spontaneous-emission characteristics are not solely determined by intrinsic materials properties; they can also be modified by the environment that interacts with these materials. In this research challenge, we are exploring nanophotonic approaches to tailoring these environments to enhance (or modify) spontaneous emission. We are investigating spontaneous-emission enhancement both from electroluminescent quantum wells used in solid-state lighting (SSL) as the primary originator of light, as well as from photoluminescent QDs, which could find use as a secondary source of wavelength down-converted light for SSL.

FDTD simulation results of the 10 µm mesh design with an electric dipole source plane in place of the InAs quantum. The inset shows the z-component of the electric field and depicts the surface plasmon mode at the metal/GaAs interface occurring at 945 cm-1

This is not a new field of research—nanophotonic approaches to enhanced spontaneous emission have been studied intensely for at least two decades. However, relevance to SSL—ultra-high-efficiency at visible wavelengths—pushes these approaches to extremes and architectures that are relatively unexplored. Ultra-high-efficiency requires extremely high enhancement factors attainable for example in high-Q photonic-crystal structures; whereas visible wavelengths require limited interaction with lossy metals.

Our current emphasis is experimental, but guided and augmented with simulations (e.g., finite-difference-time-domain, FDTD) as well as analytic and microscopic theory. We achieve control of photonic density of states (PDOS) through state-of-the-art photonic crystal nanofabrication. Our process localizes and enhances the electromagnetic field using plasmonic approaches (core-shell or planar).

Developing new nanophotonic architectures to accommodate these extreme constraints may lead to new insights of importance to SSL, and also to other technologies for which ultra-high efficiencies are important.

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Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.